In many deciduous tree crops, nutrients accumulated by leaves over the course of a season are remobilised prior to senescence and transferred to the plant's perennial framework, ready to be used the following season. There are several desirable features associated with this process: it enables the plant to retain nutrients it has spent energy on acquiring, and it contributes to reserves which sustain vegetative growth immediately after budbreak. In the case of kiwifruit, it is not clear as to whether nutrients are retranslocated from leaves after harvest, and if they are, whether the amounts retained are significant.

In conjunction with other investigations, leaves on fruiting canes were sampled from 8-year-old vines trained on a pergola trellis system. Sampling was carried out weekly, commencing 25 April 1991 (2 weeks before harvest) and concluded on 13 June (5 weeks after harvest) when few leaves remained on the vines. The results of the chemical analysis are summarised in Table 1.

For elements such as nitrogen (Fig.1a), phosphorus, potassium (Fig. 1b) and chloride, concentrations in leaves gradually declined during the sampling period, more particularly so in the weeks following harvest. Foliar concentrations for the majority of the remaining elements (Table 1) however were either the same or greater than concentrations present at the commencement of the investigation. By coupling the concentration data with measurements of leaf dry weight on each sampling occasion it was possible to determine the absolute amount of each nutrient present in a leaf, and hence the net accumulation over the course of the study (Table 1).

In only four cases was there marked loss of nutrient from leaves after fruit had been harvested (Table 1). These involved the elements nitrogen, phosphorus, potassium and chloride. The loss of nitrogen and potassium from kiwifruit leaves is not considered unusual; loss of these nutrients from leaves prior to harvest has previously been noted, but only in situations where vines had received inadequate amounts of fertiliser and were still carrying a crop. Postharvest losses of phosphorus and chloride from leaves on mature vines have not been recorded - in previous experiments leaf sampling either ceased at harvest, or leaves frosted and fell before further sampling could be undertaken. What is unusual was the lack of remobilisation of magnesium, an element typically regarded as being mobile in plant tissues. The persistent accumulation of the other elements noted here is in line with their limited mobility in phloem - the vascular vessels in which nutrients and metabolites are transported out of plant tissues.

How useful are the amounts of nitrogen, phosphorus, potassium and chloride lost from leaves? This can be checked by comparing nutrient loss from leaves (Table 1) against the total amount of that nutrient in a dormant vine. For vines containing 269 g of nitrogen, 214 g of potassium, 55 g of chloride, and 39 g of phosphorus, leaf losses account for between 17 and 24% of the respective elemental content in the over-wintering perennial framework. These figures represent an upper limit of the amounts of nutrient able to be recycled from leaves, as nutrients can be leached by rain from senescing leaf tissue towards the end of the season, as well as being returned to the vine. Nevertheless, the results suggest that nutrients remobilised from leaves may be an important component in the vine's nutrient equation and that their legacy lives on, as it were, once the leaves have died.

Figure 1. Changes in the concentration of: A, nitrogen; and B, potassium in leaves from fruiting canes of kiwifruit during the 7 weeks prior to leaf fall. Error bars represent a standard deviation either side of the concentration mean. The arrow represents the time of harvest, 9 May 1991.

Table 1 The concentration and net accumulation of macro- and micronutrients in leaves from fruiting canes during the 7 weeks prior to leaf fall.

Element	Concentration		Net accumulation by leaf falla
	25 April 1991	13 June 1991
Macronutrients	(g/kg d wt)	(g/kg d wt)	(mg per leaf)	(g per vine)b
Nitrogen	19.9	9.8	-12.6	56.7
Phosphorus	2.7	1.5	-1.5	6.8
Sulphur	6.3	5.5	0.7	-
Magnesium	6.3	6.6	3.1	-
Calcium	44.9	50.3	28.1	-
Sodium	0.3	0.2	0.0	-
Potassium	22.5	12.5	-11.3	50.9
Chloride	16.6	12.4	-2.3	10.4
Micronutrients	(mg/kg d wt)	(mg/kg d wt)	(mg per leaf)	(mg per vine)
Manganese	209	209	76	-
Zinc	31	39	29	-
Copper	10	8	0	-
Iron	140	123	20	-
Boron	54	60	36	-
aNegative numbers indicate a net loss, positive numbers a net gain in nutrient during the period 25 April to 13 June 1991. b Assumes 4500 leaves per vine, and no losses due to leaching.